Method of making mica plate



Feb. 19, 1929.

L. T. FREDERICK METHOD OF MAKING MICA PLATE Filed Dec. 25, 1926 o o o o o [N VE/v Tof-'r' Uz//s 7.' FkEDER/CK ramas, Fa. 1e, 1929i.` l y UNITED STATES- PATENT- oFFlcE.

Leurs T. FREDERIcx, or VALPARAISO, INDIANA, Assreivon To CHICAGO MlcAcoM- PANY, OF VALPARAISO, INDIANA, A CORPORATION OF ILLINOIS.

i 7 METHOD OF MAKING MICA PLATE;

Application mea December 23, 1926.: serial No. 156,629.

- Myv inventicn relates to the making of mica plate which is a known article consisting of mica flakes arranged in over-lapping relation 'and held together by shellac orother suitable binder. In order to consolidate this composite material it is necessary to vsubject it to pressure usually accompanied by heat, and difiiculty is frequentl experienced in reventing the platens o vthe press from stickor striping to the composite and loosenino' bus. reduc'- ping off some 'of the outer flakes, t

ing' the quality of the product. The purpose of myinvention is to provide a method for obviating this difficulty. f y Y The method is illustrated bythe accompanying drawings in 'Which-A Y -Figure 1 is'an 'exploded view of a piece of mica plate with two sheets on each side ldesigned to intervenebetween the product and the p latens of the press in which it is to be consolidated. Y l y,

Figure 2 isa vertical sectional view showing the platens and associated parts of apress withthe mica plate and backing sheetsin po- A sition.

Figure 3 is a perspective View of the com- I i pressed whole showing the outer stiffer backing sheets in process of removal. l Figures is a perspective view showlngthe method ofstripping off the inner highly 'flexible backin sheet from' the product.

Like numera s denote like parts throughv out the several views.

In practicing thismethod I- first assemble the mica flakes and binder to producea fplate 10. It willbe understood that the orp ,dinary binders such as shellacl are 'more or less sticky, especially when hot, and 'it has\always.

i I been a problem to prevent-the work from 'sticking tothe pressingl element after the pressing operation was completed.- Great care has been necessary to preventthe pressing elements from loosening or actually-pulling away from the 'work-portionsor all of a greater orless number of flakes. This of course produces'an/ inferior grade of product.

` According to my invention I -avoid this by taking the plate 10 ini its unpressed ferm as shown in Figure 1,*a-nd placel agalnst the faces thereof ahighly fiexi'ble. 'sheet 12 of fabric. Ihave found that a highly idesirable fabric for, the purpose is cheese cloth.' It is light in weight, comparatively inexpensive and highly flexible. On the'o'uter surface of the cheese cloth I place backingsheets 14 of much heavier and 4much less flexible material. I have found that a very suitable material for the purpose is heavy cotton duck or canvas. After the'parts are assembled in this manner they are introduced into a press. Presses for the purpose are-well known and exist in different forms. In Figure 2 I have cordance withA usual practice consolidate and flatten the mica plate to produce' a hard and strong finished product. After the pressing operation has been completed the pressure is released/,andthe work with its backing .sheets is removed from the press.

The next operation is to remove the back-l ing sheets, which 'mag be accomplished easil by simply taking hol of one corner and bend? ing it ackand leaving it off in the mannerl suggested in Fi re 3. As these outer backing sheets or pa s arestifi' compared tocheese cloth they do not flex sharply but leave the platens when forced toward each other in ac- I A aoA inner backing sheet more or less atri ht angles to the surface. 4In vother words, t e por@ ,tion momentarily leavin the inner sheet rises more or less perpendicu arly and if in direct contact with the mica Hakes Qwould have a strong tendency to loosen some of theouter flakes, bul'l by employing intervening sheets 12 no yharm is done to the product because the flakes are held by 'the inner sheets.

of them and then draws itv back at a sharp angle, as shown in Figure 4. -In other words, he strips off the inner sheet l2 by exerting asV v The next step is to remove the inner sheets. The operator first Ioosens the corner of one tension obliquely backwardv in a` directionwhich is at a comparatively sharp angle with the plane of the article. The result is that as the sheet is highly flexible there is -no appreciable `radius of curvature at the point.

Where the sheet is leaving the work, and hence the pull on the mica flakes instead of being more or lesslperpendicular to the surface of -the plate is morenearly along th'e surface of the p1ate. The Hakes, of course, are much moreable to resist a pull in their own plane than in a direction perpendicular thereto,

- and the result is that they remain tightly in vbinder is kept as low as possible.

place. llt will be understood that in the better grade of mica plate the proportion of The mica itselt has much higher dielectric properties than shellac and similar binders2 and hence it is desirable to keep the proportion ot binder as low as possible, tor illustration 2, 3 or4% by weightA oit the hnished product. With this low percentage ci? binder my method is ot Vspecial advantage in reducing as'it does, al-

most to nothing, the tendency to pull the outer flakes away trom the rest of the plate.

rlhe process adds practically nothing to the cost ot manufacture because cheese clot-h and similar materialfis cheap in itself and in most cases may be` used'over and over again.

Having thus described my invention, what l claim as new and desire to secure by Letters Patent is: l v

l. 'llhe method of making mica plate which consists in assembling micaakes in over- \5' lapping relation in association with a binder,

placing the same between two heatedplates which are adapted to be pressed together, placing a thin loosely woven and highly ilexible, non-metallic sheet ot fabric between each plate and the mica Hakes.q subjecting the whole 'to pressure and hnally stripping ed the said woven sheet by tension exerted .ohliquely backward.

2. rllhe method ot making micaplate con?4 sisting in assembling mica Hakes-in overlapping relation in association with a binderbetween upper and lower platens adapted to bepressedtogether, spreading a loosely woven sheet orn highlyenible non-metallic material' over each sident the Hakes, placing a less flexible'pad over the hrst named sheets7 subilakes and-inserting a non-metallic and lesseirible backing pad between the rst named loosely woven sheet and thee platen, subject-` ing the same to pressure, then removing the,

backing pads and then stripping the loosely woven sheetffrom the-akes at an oblique angle to the surface ofV the Hakes.

4f. 'lhe method ot making mica plate consisting in assembling mica lakes in overlappingv relation in association with the binder, placing the same between sheets ot cheese cloth, placing a backing sheet on the surface ot the cheese cloth,A subjecting the whole to pressure, then removing the backing sheet separately and nally stripping od the cheesecloth by pulling it backward at asharp plate.

5. The method 'of making mica plate consisting in assembling mica .Hakes in overlapping relation in association with a hinder,

placing a cheese cloth against each side ot the mica plate in contact with the Hakes, and placing a 'heavy textile fabric backing sheet' next to the cheese cloth, subjecting the same.-

-to pressure between heated platens, then removing the pressure and stripping ofthe backing sheets and then strippingo the cheese cloth at anacte angle to the surface of the flakes.

llin witness whereoil have hereunto subscribed my name.

4noms r. rnnnnnron I" .l

Loblique angle relatively to the surface ot the 

